The use of high-strength steels in car body construction attains ever greater importance within the scope of developing ever lighter motor vehicles. For example, sheet metal plates made of multiple-phase steels are proposed for planking parts. For planking parts made of deep-drawing materials with high hardening values, in particular, it is important that the sheet metal plate is stretched-out over an as “large-surface” as possible. For this purpose, it is state of the art to impede the sheet metal plate trailing from outside by means of a blocking step or blocking bead located on the sheet metal stopper. A disadvantage according to this method might be involved, if the sheet metal impediment remains constant throughout the deep-drawing process, particularly if the sheet metal is stretched-out beyond the 20% critical expansion in considerably deformed areas and towards the end of the deep-drawing process. In an article published by S. Beck under the heading “Steuerung des Ziehprozesses durch aktive Ziehsicken” (Controlling the Deep-Drawing Process by Active Drawing Beads) in the book “Neuere Entwicklungen in der Blechumformung” (Latest Developments in Sheet Metal Forming), editor Klaus Siegert, May 2000, the use of height-adjustable deep-drawing rods is described, which are used in order to control strains and stresses occurring in metal forming and thus to control the flow of material. Constructive solutions solely relate to a relatively expensive adjustment in height of deep-drawing rods.
Moreover, known from EP 806 256 B1 is a method for controlling the material flow during deep-drawing of work pieces like sheet metal forming blanks, wherein the frictional force between work piece and holding-down device is measured through a frictional force sensor to serve as controlling variable for a holding-down force. Also applied therein is a segmented holding-down device in order to control the holding-down force of individual holding-down device segments spread at its periphery. This solution, too, is relatively complicated.